Grinding apparatus



1366- 1965 F. o. WIENERT GRINDING APPARATUS 2 Sheets-Sheet l Filed Dec. 30

INVENTOR 7 722 2: C Zdz'eme'ri' A RNEY Dec. 14, 1965 F. o. WIENERT 3,223,336

GRINDING APPARATUS Filed Dec. 30, 1960 2 Sheets-Sheet 2 1N VENTOR F4 (1. 2 O. Wiener? RNEY United States Patent 3,223,336 GRINDING APPARATUS Fritz Gtto Wienert, Lewiston, NE. (41 Roosevelt Ave, Rte. 47, Niagara Falls, NY.) Filed Dec. 39, 1969, Ser. No. 79,669 14 Claims. ((11. 241-172) This is a continuation-in-part of Serial No. 532,983 filed September 7, 1955, which is now abandoned.

This invention relates to grinding apparatus and is particularly, though not exclusively, concerned with rotary grinding mills of the type in which balls or similar grindin g elements are used.

In conventional tumbling mills the grinding is substantially all done by those grinding bodies, such as balls, which cascade toward the bottom of the mill as it is rotated. In the noncascading portion of the mass of grinding bodies, however, these bodies are substantially at rest with respect to adjacent bodies and consequently have little grinding action.

It is an object of the present invention to provide a mill of the type described in which substantially all of the grinding bodies are so moved, either with respect to the mill or to each other, that they perform a substantial grinding action.

Another object of the present invention is to provide a mill of the type described which has an increased grinding capacity.

A further object of the invention is to provide a mill of the type described which has a high efficiency.

Still another object of the present invention is to provide a mill of the type described which may be operated in different ways to achieve maximum efficiency.

A further object of the invention is to provide processes of milling which produce improved results.

Yet another object of the invention is to provide apparatus that can be used efficiently for dispersion of solid particles in liquid media and for dry mixing of granular materials.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a longitudinal sectional view, somewhat conventionalized, of a grinding mill constructed in accordance with the present invention;

FIGURE 2 is a fragmentary, longitudinal sectional view of a modified form of mill in accordance with the invention;

FIGURE 3 is a detail view of a rotor as used in a mill according to the invention;

FIGURE 4 is a detail view of a modified form of rotor,

FIGURE 5 is an enlarged detail view showing in elevation still another modmed form of rotor;

FIGURE 6 is a sectional view of the rotor illustrated in FIGURE 5; and

FIGURES 7-9, inclusive, are fragmentary, longitudinal sectional views of additional modified forms of grinding mills according to the present invention.

FIG. is a vertical sectional view through the mills shown in FIGS. 1, 2 and 7 through 9 illustrating exemplary openings or orifices in the partitions within the mills.

The objects of the present invention set forth above are accomplished by providing in a mill having an elongated shell adapted for use with freely movable grinding bodies such as balls, pebbles or lumps of the material being ground, a plurality of communicating, axially arrayed grinding zones and means by which there is 'ice to a substantial portion of the grinding bodies in each of said zones compressive force directed longitudinally of said mill shell and force directed transversely of said shell whereby a substantial number of said grinding bodies are caused to move in paths which are the resultants of motion arcuately, radially, and longitudinally with respect to said shell. Such means comprises essentially one or more disc-carrying rotors within the mill, said rotor or rotors and the drum or shell of the mill being so mounted and arranged as to permit their relative rotation around the longitudinal axis of the mill. The several grinding zones are preferably formed by annular partitions within the mill shell or drum and at least one rotor is usually aranged within each of said zones. The discs of these rotors are angularly disposed obliquely to said axis of rotation so that when the discs and the bed of grinding bodies in the grinding zones move relatively to each other the grinding bodies are acted upon by the forces described above.

The specific nature of the invention will be made more clearly evident by reference to FIGURE 1 which shows in a somewhat simplified and conventionalized manner a preferred mill construction. In FIGURE 1, the numeral 11 indicates a suitable base which may be a platform, a floor, or other desired structure upon which the supporting pedestals 12 and 13 are mounted. The mill itself is a hollow drum 14 comprising a cylindrical shell 15 and end heads 16 and 17. Within the drum are a plurality of transverse, annular partitions 13 having aligned openings 19 around the axis of rotation of the mill. These partitions are secured to the interior of the shell 15 at points around their peripheries by any suitable means, such as welds, bolts, or the like, and form a series of axially arrayed, communicating compartments 20 in the drum, each of which may constitute a grinding zone. The heads 16 and 17 of the drum 14 are provided with axiallyproiecting, hollow trunnions 21 and 22, respectively, that are rotatably supported in bearing portions 23 provided at the upper ends of the pedestals 12. A ring gear 24 suitably attached to the drum is adapted for cooperation with any conventional gearing and power source to permit rotation of the drum in either direction. Connected to the hollow trunnions 21 and 22 by suitable slip joints 26 and 27, respectively, are a feeder 28 and a discharge duct 29.

Extending axially of the mill through the openings 19 in the partitions 18 and projecting from the drum at its ends through the feeder 28 and the duct 29, respectively, is a shaft 32 which is journalled in bearings 33 carried by the pedestals 13. A gear 34 suitably secured to the shaft 32 at one end of the latter provides means which may be operatively connected with any convenient power source to permit rotation of the shaft in either direction. Within the drum 14 the shaft 32 carries a plurality of rotors 36 comprising rigid discs 37 which are fixed by suitable means to the shaft for rotation therewith in the compartments 20. The discs 37 are essentially solids of revolution, i.e. are formed by revolution of a line around an axis, and have axes which are different from that of the shaft 32. Consequently, as the shaft rotates, the discs 37 have a wobbling or nutating movement. The rotors 36 are so positioned on the shaft 32 that the disc 37 of each of the rotors is angularly arranged at an angle other than with respect to the discs of adjacent rotors. Smoother operation, more even power demand, and reduction or elimination of end thrust results from simultaneously imparted this. Preferably, the discs 37 are only slightly smaller in a radial direction perpendicular to the shaft than the inside diameter of the shell 15, but, if desired, greater peripheral clearance may be provided for them by reducing their radial dimensions but only so as to provide preferably a clearance between the shell and periphery of the discs which is substantially constant, thereby preventing the passage of material therebetween in excess of a predetermined size controlled by the dimension of said clearance space.

Conventional flights or conveyor screws 38 and 39 are provided in the hollow trunnions 21 and 22, respectively, whereby the material placed into the feeder 28 is moved into the mill and the finely milled material or product is conveyed to the discharge duct 29. A discharge grate 40 is also provided at the entrance to the hollow trunnion 22 to prevent passage of the larger grinding bodies and oversize particles of material. This grate may be of any suitable or conventional design and construction.

Some possible variations in mill construction are illustrated in FIGURE 2. Here the cylindrical shell 42 of the mill drum 41 is provided with heads 43 and 44 that are inclined obliquely with respect to the longitudinal axis of the mill and that carry hollow trunnions 46 and 47, respectively. The latter are adapted for support in suitable bearings (which may, if desired, be like those shown in FIGURE 1) to permit rotation of the drum by any conventional or suitable means (not shown). At spaced, longitudinal intervals along the inside of the drum 41 there are provided transverse, annular partitions 49, also inclined obliquely with respect to the axis of the shell 42, which form a series of axially arrayed, communicating compartments 50 which may constitute grinding zones. The partitions 49 are secured to the interior of the shell 42 at points around their peripheries by any suitable means, such as welds, bolts or the like, and have aligned openings 51 around the axis of rotation of the mill.

A shaft 53 extends axially-through the drum 41, passing through the openings 51 in the partitions 49, and carries thereon by suitable means a plurality of rotors 54 for rotation therewith in the cylindrical compartments 50. Like the rotors 36 in FIGURE 1, the rotors 54 include rigid discs 55 that are essentially solids of revolution, the axes of which are different from that of the shaft 63. Thus, as the shaft rotates, the discs 55 have a wobbling or nutating movement. The mill shown in FIGURE 2 may, of course, also be provided with conventional or other suitable inlet or feeder, discharge grate, discharge duct and flights or conveyors. The shaft 53 is provided externally of the drum 41 with suitable bearings and means for producing rotation (not shown).

FIGURES 3 and 4 illustrate in more detail two of the many possible ways of constructing rotors of the type shown as 36 and 54 in FIGURES 1 and 2, respectively. In FIGURE 3 the rotor 56 comprises a rigid, annular disc 57 supported by a spider 58 on a sleeve 59. The latter may be secured in any suitable manner to a shaft 60. The annular disc, spider, and sleeve may be formed integrally or may be formed separately and secured together in any desired way, by welding, for example. In some instances, however, the disc and spider may advantageously be bolted together for ease in replacing a worn annulus. In any event, it will be seen that in this construction openings 65 are provided through the rotor adjacent the center thereof between the arms of the spider 58. If desired, other holes or orifices (not shown) may be provided through the disc 57. Such holes, if provided, and the openings 65 through the rotor allow and facilitate passage of fine milled material through the mill.

In FIGURE 4 the rotor 61 is of somewhat different construction in that the sides of the rigid disc 62 thereof are not substantially parallel. As shown, a cross section of the disc 62 has the appearance of a double wedge, the sides converging at their outer ends. The disc is carried i by a sleeve 63 which may be integral therewith, as shown, or if desired may be separately formed. The sleeve 63 is adapted to be mounted on a shaft 64. As in the construction illustrated in FIGURE 3, holes or orifices (not shown) may be provided through the disc 62.

The sleeves 59 and 63 may be secured to the shafts on which they are mounted by any suitable means. Preferably, they are fastened thereon by keys, set screws, pins, or the like (not shown) so as to be readily removable from the shaft for repair or replacement. For this purpose the sleeves may, if desired, be split. If desired, however, the sleeves may be welded, brazed or otherwise more permanently secured on the shafts or the rotors may be directly welded or otherwise suitably fastened to the shafts without the use of sleeves.

As indicated above, the discs of the rotors carried by the rotatable shaft in a grinding mill according to the present invention may have diameters substantially equal to the diameter of the interior of the cylindrical shell of the mill. However, if the discs are circular in section normal to their axes and are inclined with respect to the axis of the shell, there is more space between the shell and the top and bottom (as shown, for example, in FIG- URE l) edges of the discs, i.e. the edges nearest the rotatable shaft, than between the shell and the side edges of the discs. Where the mill is of relatively small diameter and the discs are inclined at an angle of no more than about 8l0, for example, with respect to a plane normal to the axis of the shaft and shell, this difference in clearance is not of substantial importance. But where the angle of inclination of the rotatable discs is greater or where the mill drum has a relatively large internal diameter, the larger clearance resulting at the top and bottom edges of the discs may be undesirable.

If desired, therefore, the rotor discs may be formed to have an elliptical section normal to their axes so as to reduce such inequalities in clearance. While this can be done by merely changing the shapes of the discs, it is preferred in many cases to employ a construction like or similar to that shown in FIGURES 5 and 6. There the rigid disc 66 of the rotor is an annulus attached at its center by welding or the like to a mounting sleeve 67. At its top and bottom edges (as shown in FIGURES 5 and 6) the disc 66 is provided with reinforcing wear plates 68 secured in any suitable manner, for example, by rivets or counter sunk head bolts 69, to the inner faces of the central portion of the disc. By inner faces is meant those faces nearest the axis of rotation of the rotor. The outer edges of the plates 68 extend beyond the edges of the central portion of the disc and are so curved as to cause the rotor to be elliptical in section normal to the axis of the disc thereby making the clearance around the rotor uniform when it is mounted for rotation in or with respect to a cylindrical mill drum. If desired, of course, the disc 66 may be formed with orifices or holes (not shown) to facilitate passage through the mill of fine material. It will be evident that reinforcing wear plates of the character just described may also be used with elliptical discs or, without changing their peripheral shape, with round discs.

FIGURES 79, inclusive, illustrate examples of other mill constructions comprehended within the teaching of the present invention. In the embodiment shown in FIG- URE 7 the rotatable drum 86 with trunnions 81 is provided with spaced, annular, transverse partitions 82 in its interior. The partitions form, with the drum heads 83, a series of axially arrayed, compartments 84, communicating through axial openings 85 in the partitions. A rotatable shaft 86 carries spaced rotors 87 thereon for rotation with the shaft in the cylindrical compartments 34 Both the partitions 82 and the rigid disc portions 38 of the rotors 87 are inclined obliquely with respect to the axes of the drum 8t) and the shaft 86. Although as shown the angles of inclination are different, they may, of

3 course, be the same. As will be evident, the mill of FIG- URE 7 is very similar to that shown in FIGURE 2.

The mill of FIGURE 8 is illustrative of the possibilities in varying the angles of the interior partitions to obtain compartments of different shapes. Here the rotatable drum 9% has heads 91 of frustoconical cross-sections carrying trunnions 92. The drum is also provided with longitudinally spaced, annular, transverse partitions 93 secured by suitable means, at points around their peripheries, to the interior of the cylindrical drum shell and having axial openings $8. The central partition is arranged normal to the longitudinal axis of the shell while those partitions adjacent to the heads 91 are inclined obliquely with respect to said axis. The cylindrical compartments 94 thus formed consequently vary in length at different points around their peripheries. The rotatable shaft 97 is provided with a plurality of rotors 96 fixed thereto, one rotor being located in each compartment. As illustrated, the rigid disc portions 95 of the rotors are also inclined obliquely with respect to the longitudinal axes of the shaft 97 and the drum 90. In this respect this mill is similar to the mills shown in FIGURES 1 and 2.

As will be evident, in the mills illustrated in FIGURES 7 and 8 the compartments formed by the annular partitions may constitute grinding zones. Also, it will be understood that in the constructions of these figures as well as that shown in FIGURE 9, there may be provided complementary details such as suitable feed and discharge grates, flights or conveyors, and rotating means for drums and shafts. Such details may be like those shown in FIGURE 1 or of any other conventional or suitable designs.

The mill structure shown in FIGURE 9, although quite similar to the embodiment illustrated in FIGURE 1, differs somewhat in principle. It comprises a rotatable or non-rotatable cylindrical drum tilt: having, normal to its axis, heads 1G1 carrying trunnions 192. Within the drum, two cylindrical compartments 103 are formed by transverse annular partition 104 fixed at points around its periphery to the interior of the drum shell and arranged normal to the drum axis. In each of the compartments 103, which are in communication through axial opening 198 in the partition 194, are a plurality of rotors 105 secured to shaft 1% for rotation therewith. The rigid discs 187 of the rotors are inclined obliquely with respect to the axes of the drum and the shaft, and the discs are differently inclined, i.e. non-parallel. As shown, starting from either end each of the discs is oriented 90 from the preceding one. In each compartment the grinding zone for each rotor may be considered to be bounded longitudinally by the other rotor and the nearest transverse portion of the drum, i.e. a head 101 or the partition 164. Obviously, if desired, mills may be constructed with only one or a plurality of rotors and with no stationary partitions, the grinding zone or zones being formed by the mill heads or, where a plurality of rotors is used, by the rotors and such heads or by the rotors themselves.

Mills, according to the invention may be operated for comminuting material in a number of different ways. For example, with a mill such as is shown in FIG. 1, a preferred manner of operation is as follows:

The mill drum is loaded with a bed of balls of desired material and size, shown symbolically by the balls 75, and the material to be ground is introduced through the feeder 28. The shaft 32 is then rotated while the drum 14 is held stationary. It will be evident that as the rotors 36 on the shaft turn within the grinding zones formed by the compartments 29 the discs 37 of the rotors will exert force on a substantial number of the balls in the mill. In each grinding zone the balls are separated by the rotor 36 into two, preferably substantially equal, portions. As the rotor in each compartment turns the disc 37 thereof exerts on a substantial number of the balls in the two portions a compressive force longitudinally of the shell 15. This compressive force is applied alternately to the two portions and simultaneously with its application the disc also exerts, on a substantial part of the same portion of the balls, 21 force directed transversely of the shell. Since the balls in each portion of the grinding zone are constrained by the adjacent partition or end wall, as the rotor revolves the level of the balls in each portion alternately rises and falls as the space available therefor in the bottom portion of the grinding Zone decreases and increases. Because of this, and the curvature of the sides of the grinding zones, a substantial number of balls in each portion of each zone is successively given arcuate, radial, and longitudinal motion with respect to said shell. Consequently, the path of each ball in each grinding zone is influenced directly or indirectly by the forces exerted by the rotor in said zone and is a resultant of the motions described above. It will be evident that the path of each ball in the mill will be unique since the motions mentioned above as Well as other influences, for example, gravitation, the percentage of the mill capacity filled with balls, the type of material being ground, and the speed of rotation of the shaft 32, will act differently on each ball.

The material fed into the drum for milling will, of course, be subjected to a combination of forces as a result of the movement of the grinding balls described above, as well as the gravitational force due to the superincurnbent weight of the mass of balls and material in the mill. The forces due to movement of the balls by the rotors cause pressures on particles of the material between balls which are much greater than the gravitational force thereon and which produce rupturing of such particles. This action is in addition to the abrading or shearing action that results from the sliding or rolling movements of the various surfaces within the mill relative to each other. Such abrading action is, however, more intense than in conventional mills because of the greater pressures existing between certain of the grinding balls as the rotors turn within the compartments.

A second method of operating the grinding mill illustrated in FIGURE 1 is to maintain the shaft 32 stationary and rotate the drum 14 by any suitable or conventional means such as by the ring gear 24 attached thereto. In this method of operation the balls, symbolically represented by the balls 75, in each grinding zone formed by the compartments 29 is given an arcuate movement by the rotation of the drum but the paths of the balls are noditied as a result of the irregular shape of the spaces on each side of the rotor in each compartment. Hence the paths are not such as would result in the absence of the rotors and better comminution of the material to be ground is obtained than in a conventional rotating mill because the balls have more movement with respect to each other and are subject to different forces.

The most eificient operation according to the method just described, where the drum alone rotates, requires the use of a relatively high rotational speed for the drum. Speeds of rotation are preferred which in a conventional ball mill would cause undesirable centrifuging of the balls. In mills according to the present invention, when operating as described, the presence of the rotors and parti tions prevents or minimizes centrifuging while at the same time permitting a considerable amount of cascading movement of the balls relative to each other. In a modification of this method lower drum rotational speeds may be used, while maintaining a high efhciency, if the shaft 32 and the rotors 36 thereon are made to rotate in the opposite direction to the drum.

Still another method of operating the mill shown in FIGURE 1 requires rotation of the drum 14 and the shaft 32 in the same direction but at different speeds. This method is not generally preferred but may be used to advantage to facilitate migration of the milled product through the mill or to prevent possible packing in the corners of the compartments. It may also be employed in starting a large mill to avoid overloading the driving motor or motors. Thus, for example, in starting a loaded mill both the drum and shaft may initially be rotated at the same speed in the same direction. Then with the shaft continuing rotation at constant speed, the drum may gradually be slowed down until it stops, the further operation of the mill being in accordance with the first method of operation described. Also, of course, by slowing the shaft while continuing constant speed rotation of the drum, operation by the second method described above can be accomplished without an excessive initial power demand.

The mill illustrated in FIGURE 2 may be operated in substantially the same manner as the mill of FIGURE 1. In this construction the angular disposition of the partitions 49 and the end plates 43 and 44 will result in the movement of the balls (shown symbolically at 75) in each grinding zone being different in the two portions on either side of the rotor therein. Consequently, the grinding action will be somewhat different on each side of each rotor. The angles of the drum heads 43 and 4-4, the partitions 49, and the discs 55 of the rotors 54 may be altered as desired in the construction shown in FIG- URE 2. However, as will be evident, if the rotor discs are normal to the axis of the shaft 53 no substantial grinding action will take place upon rotation of the shaft alone. On the other hand, operation by rotating only the drum will be productive of greater movement of the balls in each grinding zone than with the mill illustrated in. FIGURE 1 because of the angularly placed partitions.

As pointed out above, the mills illustrated in FIGURES 7 to 9 resemble those shown in FIGURES 1 and 2. The mill of FIGURE 7 may be operated in a manner very much like the mill of FIGURE 2. The mill of FIGURE 8, resembling both those of FIGURES 1 and 2, will, in operation, be similar to both. The mill shown in FIG- URE 9 may be operated like the mill of FIGURE 1 with similar movements of the balls between the rotors and between the mill heads and the rotors but, because of its diiferences in construction, will produce somewhat different results. It will be clear that any of the embodiments illustrated may be operated in any of the ways described in connection with the mill shown in FIGURE 1.

From the foregoing description it will be evident that there may be considerable variation in construction of grinding mills according to the invention while retaining the principal advantages of the invention. Thus, the shape of the mill drum can be varied to provide heads normal to the longitudinal axis thereof, fiat heads at an angle to such axis, or frustoconical heads, the heads being secured to the shell in any suitable manner. Also, obviously, the drum may vary in diameter and/ or length and in the number of compartments formed therein by the annular partitions secured to the inside of the shell. The drums, of course, may be formed of any suitable material and may be provided with any conventional means for rotation and with such conventional adjuncts (not shown) as inspection or filling holes, linings, etc. It will also be seen from the description of the operation of the mills according to the invention, that certain details of construction of such mills will be determined by the intended manner of operation. Thus, for example, if it is desired to operate a mill exclusively by the first method described above, there is no reason for providing rotating means for the drum. Indeed, as pointed out hereinafter, the shape of the drum may, if desired, be modified in such case.

The transverse partitions employed in mills according to the invention may be secured to the interior of the mill drum in any suitable manner. While these partitions are illustrated as flat, annular dsics, it will be understood that they can have other shapes. For example, they may be thicker at their outer edges than at the center to give greater strength and, if desired, may have curved or angu- 0 lar faces. In any case, it is preferred that each such partition be so formed that a plane passing through the middle of the inner and peripheral edges thereof will be included within said partition. As illustrated, the partitions can be arranged at various angles to the longitudinal axis of the drum. In many cases where the partitions are not normal to the axis of the drum an angle of about 10 from normal is preferred.

The central openings in the partitions must obviously be large enough to provide clearance for the rotatable shaft passing therethrough and preferably are somewhat larger to permit passage of fine material from one grinding zone to another, as clearly shown in FIGS. 1, 2, 7, 8 and 9. Alternatively, perforations 110 may be provided in the partitions or space may be provided at one or more points around the outer edges of the partitions, as shown, in exemplary manner only, in FIG. 10, or a combination of any two or more of these expedients may be employed to make such passage possible. In any case the dimensions of the spaces or openings provided in a partition should be such as to prevent passage of the smallest grinding body used in the adjacent grinding zones if migration from compartment to compartment of grinding bodies or coarse lumps of material undergoing reduction is to be avoided.

The lengths of the compartments in the mill drum, i.e. the longitudinal spacing between the annular, transverse partitions and between the drum heads and the end partitions, are preferably such that the minimum distances between the end walls of each compartment and the disc therein, as the rotor, of which it is a part, rotates with respect to the drum, are equal to at least twice the diameter of the largest ball or grinding body used therein. On the other hand, while it is preferred to have the compartments somewhat longer than this, they should not be so long that during operation of the mill no substantial movement of the grinding bodies results from the interaction of the rotors and partitions therein. Since the amount of such movement is dependent to some degree upon the size of the grinding bodies used, therein number, the angles of the rotors and partitions, and the speed of rotation, maximum desirable compartment lengths will vary with conditions. The same considerations also determine the desirable longitudinal spacing of rotors with respect to each other and to elements of the drum when rotors are not separated by partitions as in FIGURE 9.

In FIGURES 36 some variations in construction of rotors for use in mills according to the invention are illustrated. It will be understood, however, that any mill constructed in accordance with the invention may comprise rotors of any desired design and that, if desired, the rotors as well as the partitions in such a mill may be formed of segments or other elements which are assembled together by suitable means in the desired shape, leaving, if desired one or more gaps, slots, or the like for passage of material. Because of the high stresses to which the rigid discs are subjected when rapidly rotated in a loaded mill, types similar to that shown in FIGURE 4 are often desirable since they are stronger and less liable to distortion or other damage. It will, however, be evident that many modifications are possible. The discs of such rotors, as indicated above, may be provided with openings therethrough and may be shaped in various ways. For example, the disc 62 in FIGURE 4 could, if desired, have curved faces instead of straight ones. Essentially, however, aside from deviation to provide, where desired, an elliptical shape for the reason discussed above, the discs are solids of revolution formed by the revolution of a line about an axis. Further, as shown each disc is disposed at an angle other than to the axis of the shaft on which it is mounted. It will be understood that with some types of construction, for example, where the disc is welded or brazed directly to the shaft, the distinction between disc and rotor vanishes since the disc will comprise the whole rotor. In any event, except in rare instances when it is desired, as suggested above, to operate a mill with obliquely inclined partitions by rotating the drum only a characteristic common to the discs with which this invention is concerned is that when such a disc is rotated about the axis of the shaft on which it is mounted, every point on the surface of the disc revolves around said axis in a circular path while the disc, as a while, has a nutating or wobbling motion.

It will be observed that in FIGURES l, 2, 7, S and 9 the mill drum and the longitudinal shaft passing there through are coaxial. This is ordinarily the preferred construction. However, in mills desi ned to operate with rotation of the shaft and the rotors thereon only, the shaft may, if desired, be parallel to but below the longitudinal axis of the drum and/or a portion of the drum may be nonsymrnetrical and/or noncylindrical. Thus, for example, the top of the drum may in such a case be formed to provide a rectangular opening and be provided with a cover. In such cases, obviously, the stationary partitions, if any, within the drum will have suitable shapes and are not necessarily annular discs.

As shown in the drawings, the angles of the rotor discs with respect to a plane normal to the axis of rotation of the rotors may vary substantially and the discs and interior partitions may also be at different angles. The discs in any particular mill may be parallel, as in FlGURE 2, or may be nonparallel as in FIGURE 1, and, if desired, at different angles with respect to the above-mentioned plane. The smaller the angles of the discs with respect to the above-mentioned plane, the less movement of the grinding bodies is produced during each revolution of the rotor. Other factors being unchanged, a reduction in disc angle must be accompanied by an increase in rotational speed to obtain equivalent grinding results. On the other hand, the power required for operation increases with an increase in disc angle. Thus, the choice of disc angle involves consideration of the factors involved and a balancing of advantages and disadvantages. In general, angles of less than about 35 are not desirable since the movement of the grinding bodies by the rotors is too small. In fact, as will be evident, there will be no substantial comminuting action where the rotors only are rotated if the discs of the rotors are normal to the axis of rotation of the latter.

It is preferred to have the rotors so mounted on their shaft that adjacent discs are not parallel one to another. Such arrangements are illustrated in FIGURES 1,. 8, and 9. In the first two of these figures, adjacent discs are shown as positioned 180 from parallel, while in the last, starting from either end, each disc is oriented 90 from the preceding and following ones. Nonparallel disc arrangements are preferred as the load is more evenly distributed over each revolution of the rotor shaft. Moreover, there is less end thrust on the shaft since at any specific point of each revolution the longitudinal force exerted by rotation of one disc on matter in the mill at least in part balances an opposing force exerted by another disc. If desired and convenient, of course, adjacent discs may be oriented at any other angle, 90 and 180 differences being merely illustrative.

The grinding bodies employed in mills according to the present invention may be of any desired type, pebbles and metallic or ceramic balls or shaped bodies being usable as well as lumps of the material undergoing reduction, whether preselected for size or of random size introduced as part of the feed to the mill. More or less rounded bodies such as pebbles or balls will, however, be moved more easily by the rotors in the manner described above than bodies which are predominantly flat or angular in shape. Except when otherwise clearly indicated, where reference is made in this specification or the accompanying claims to grinding bodies the term is intended to have a broad meaning and to include anyone or a combination of solid bodies of the types mentioned above.

As indicated above, when operating mills according to the present invention by rotating the shaft and rotors, it is preferred to use a shaft rotation speed that is relatively high with respect to the speed, if any, of the drum. It has been found that, other factors equal, the grinding capacity, i.e. the rate of throughput which results in a milled product having the desired particle size or range of particle size, increases with increased rotor shaft speed. Accordingly, shaft speeds up to those which cause an undesirable power load may be employed. Where both the rotor shaft and the drum are rotatable, results similar to those produced with relatively high shaft speeds and a stationary drum can be obtained with lower speeds of the shaft if the drum is rotated in the opposite direction. This method of operation also insured complete and continuous turnover of the entire mass in the mill.

It will be understood that novel mills according to the present invention may be used for either wet or dry grinding and that either continuous or batch operation in either an open or a closed circuit system may be employed. Conventional adjuncts to mill systems such as magnetic separators, screens, classifiers and passage of fluid through the mill to remove fine particles may also be used and necessary modifications of the feed and/or discharge mechanisms can be made to permit such use.

In conventional tumbling mills cascading of the grinding bodies and material being ground provides a very large part of the grinding or comminuting action. In mills according to the present invention, however, the action of cascading grinding bodies is much less significant since, because of their novel construction, the balls or other grinding bodies are subjected to more movement with respect to each other and to the mill. Consequently, the present invention provides a mill that may be changed, with balls or other grinding bodies in an amount such that the bulk volume of the grinding bodies is in excess of 50% of the mill volume and which still operates satisfactorily when the bulk volume of the grinding bodies is as great as 90% of the mill volume. This is in distinct contrast to the %50% charge which is usual with conventional tumbling mills. It is to be noted that the greater volumes occupied by the moving mass in the present novel mills increase the grinding capacity, whereas the grinding capacity of conventional mills decreases when the grinding bodies and charge therein occupy more than about of the mill volume.

On the other hand, mills according to the present invention may be operated with less than what is generally regarded as a normal charge. With relatively high rotor speeds in mills with loadings of from 10% to 35% of the mill volume the grinding action of the mill is somewhat modified. While the grinding action still takes place largely between the grinding bodies in the mass, there is more freedom of movement of the guinding bodies and their action is aparently characterized by recurring momentary separation of at least a portion of the grinding bodies, one from another, followed by rapid and violent collisions of the bodies as they are propelled together by the rotating, angularly disposed discs on the rotor shaft. The movement of the grinding bodies as they thus alternately separate and collide is therefore more lively than with a more fully loaded mill and impact between the bodies accounts for a part of the comminuting action. With relatively low loadings less power is required for a given period of operation than with more fully loaded mills and in some circumstances this factor makes the use of low loading desirable.

In mills constructed in accordance with the present invention grinding is carried out in one or more axially arrayed grinding zones each of which comprises a rotor. It will be understood that each zone may, in some ways, he considered a separate mill in which the type and arrangement of the rotor therein, the size and type of grinding bodies employed, the degree of loading with grinding ll bodies, and the distribution of such bodies with respect to the rotor may vary from zone to zone.

This variation may, if desired, be major. Thus, in one grinding'zone, for example, the zone adjacent a mill head, there may be no grinding bodies on the side of the rotor facing said head, all of the grinding bodies in the zone being on the other side of the rotor, while in one or more other zones the grinding bodies are divided into two portions by the rotor. Further, for example, in one zone a few relatively large grinding bodies may be employed while in another zone a large number of relatively small grinding bodies may be used. Obviously, if desired, grinding bodies of different sizes may be mixed and in a single grinding zone the bodies on one side of the rotor may be different in size from those on the other side thererof. With loadings of about 40% or more a majority of the grinding bodies in each zone will be out of contact with the mill shell at any specific time. When the shaft and its attached rotors are rotated with respect to a stationary drum the rotor in each grinding zone will exert successively on a substantial part of each portion of grinding bodies in said zone simultaneous longitudinal compressive force and force transversely of the mill shell thereby, in conjunction with other mill structure, causing motion of a substantial portion of the grinding bodies arcuately, radially, and longitudinally with respect to the shell. It will be apparent that with other methods of operation or changed conditions the grinding action will be different to some extent and may be more complex.

It will be evident that the novel mills of the present invention are adapted for use in mixing and agitating materials therein even when it is not intended that any substantial reduction in particle size of such materials shall be accomplished. Thus, a finely comminuted material may be admitted to the mill with the charge so that it will be mixed homogeneously with the material being ground in the comminuted discharge. Such mixing or agitation may be carried out, even in the absence of grinding bodies, in some or all of the compartments of the mill, with dry, granular or powdered materials or with granular or powdered materials that are wetted by or mixed with Water or other suitable liquids. Also, of course, a liquid may be fed to a mill wherein one or more granular or powdered materials is being agitated so that the liquid is thoroughly mixed with and distributed in the mass. Examples of the several procedures mentioned above, are the blending together of pigments for use-in inks, paints, and the like; the mixing of various constituents in ceramic slipcasting compositions; and the dispersion of pigments in liquid or plastic vehicles.

Mills according to the present invention may be operated in any desired manner in carrying out the mixing or agitating functions described above. It is believed, however, that the most thorough mixing takes place when there is the most activity in the mass of material in the mill. Accordingly, operation of a mill like that shown in FIGURE 2 with the rotor and the drum rotating in opposite directions would in many cases produce the best results.

Although a number of constructions illustrative of the present invention have been described above, it will be evident that to those skilled in the art other modifications, variations and additions which do not depart from the principles of the invention are possible. it is, therefore, intended that the invention shall be broadly construed and that it shall not be considered as restricted except as limited in the appended claims.

I claim:

1. A grinding mill comprising an elongated shell, a grinding zone in said shell arranged to contain a bed of material to undergo treatment intermixed with a plurality of freely movable grinding bodies, a substantial portion of said grinding bodies being out of contact with said shell at any specific time, material moving means within said shell comprising a shaft extending longitudinally of said elongated shell and a rigid disc fixed to said shaft and disposed obliquely thereto, said disc being disposed at least partially within said bed When said mill is operating, supporting means for said shell and material moving means operable to permit relative rotatable movement therebetween about the axis of said shell, and drive means operable to eifect such relative rotation therebetween, imparting to at least a substantial portion of said grinding bodies arcuate tumbling movement about the axis of said mill and oscillatory axial movements of substantial extent in opposite directions with respect to the longitudinal axis of said mill.

2. A grinding mill as set forth in claim 1 in which said disc is elliptical and the perimeter thereof is spaced from said shell a substantially constant distance less than the diameter of said grinding bodies.

3. A grinding mill comprising an elongated shell, means therein defining a plurality of communicating, axially disposed, grinding zones in said shell, each said grinding zone containing a plurality of freely movable grinding bodies, a substantial number of said grinding bodies being out of contact with said shell at any specific time during operation of the mill, and material moving means comprising a shaft extending longitudinally through said grinding zones and substantially coaxial With said shell, said shell and shaft being supported for relative rotation therebetween, driving means operable to eifect said relative rotation therebetween, at least a single rigid disc in each grinding zone fixed upon said shaft obliquely thereto, said discs being at least partially within said bed of grinding bodies Within said Zones and said material moving means being operative during relative rotation between said shell and shaft to impart simultaneously to a substantial portion of said grinding bodies within each of said grinding zones compressive force directed longitudinally of said shell and also force directed transversely to the axis of said shell, whereby a substantial portion of said grinding bodies are caused to tumble and move arcuately and radially and also longitudinally to a substantial extent with respect to said zones within said shell.

4. In a grinding mill, the combination of an elongated cylindrical shell, means for introducing material into and removing material from said shell; said shell containing a plurality of axially spaced transverse partitions, said partitions being provided with orifices and being attached to said shell at their peripheries, thereby dividing the interior of said shell into a pluralty of axially disposed compartments communicating with each other longitudinally, each of said compartments being adapted to contain grinding bodies; a shaft extending longitudinally through said shell and said compartments and said shaft and shell being mounted for relative rotation about the axis of said shell, drive means operable to cause relative rotation therebetween, a plurality of rotors secured to said shaft and each comprising a rigid disc, each of said discs being substantially planar and symmetrically disposed obliquely to the axis of said shaft and peripherally spaced radially substantially uniformly from said shell, at least one of said rotors being located within each of said compartments.

5. A grinding mill as set forth in claim 4 further characterized by said orifices in said partitions being adjacent the peripheries thereof and operable to permit passage therethrough of ground material of predetermined maximum size controlled by the size of said orifices.

6. A grinding mill as set forth in claim 4 further characterized by at least some of said compartments having a plurality of oblique discs therein and said discs being nonparallel to each other.

7. A grinding mill as set forth in claim 4 further characterized by at least some of said compartments having a plurality of oblique discs having substantially equal obliquity with respect to the shaft but said disc being arranged upon said shaft at different rotary angular re- 13 latiions, thereby rendering said discs non-parallel to each at er.

8. A rotor for a grinding mill adapted to be mounted on a shaft within said mill, said rotor comprising a mounting sleeve and an elliptical disc carried by said sleeve and disposed obliquely to the axis thereof, said disc comprising a central portion and reinforcing wear plates rigidly attached to said central portion and the periphery of said disc and attached Wear plates having a substantially constant radial dimension with respect to the axis of said sleeve in directions perpendicular to said axis.

9. A grinding mill as set forth in claim 1 in which a plurality of rigid discs are secured to said shaft and arranged relative to each other so that at least some of said discs are nonparallel with an adjacent disc.

10. A grinding mill as set forth in claim 1 in which said disc has openings therein through which finer size ranges of milled material passes, thereby to facilitate the passage of said material through the mill.

11. A grinding mill as set forth in claim 4 in which at least some of said discs are nonparallel to each other.

12. A grinding mill as set forth in claim 4 in which said partitions are substantially parallel to each other.

13. A grinding mill as set forth in claim 12 in which said partitions are normal to the axis of said shaft.

14. A grinding mill as set forth in claim 4 in which said partitions are inclined obliquely with respect to the axis of said shaft.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS Australia. Germany. Germany. Germany. Germany. Germany. Great Britain. Great Britain. Italy.

25 I. SPENCER OVERHOLSER, Primary Examiner.

EDWARD 1. MICHAEL, ROBERT A. OLEARY,

Examiners. 

1. A GRINDING MILL COMPRISING AN ELONGATED SHELL, A GRINDING ZONE IN SAID SHELL ARRANGED TO CONTAIN A BED OF MATERIAL TO UNDERGO TREATMENT INTERMIXED WITH A PLURALITY OF FREELY MOVABLE GRINDING BODIES, A SUBSTANTIAL PORTION OF SAID GRINDING BODIES BEING OUT OF CONTACT WITH SAID SHELL AT ANY SPECIFIC TIME, MATERIAL MOVING MEANS WITHIN SAID SHELL COMPRISING A SHAFT EXTENDING LONGITUDINALLY OF SAID ELONGATED SHELL AND A RIGID DISC FIXED TO SAID SHAFT AND DISPOSED OBLIQUELY THRETO, SAID DISC BEING DISPOSED AT LEAST PARTIALLY WITHIN SAID BED WHEN SAID MILL IS OPERATING, SUPPORTING MEANS FOR SAID SHELL AND MATERIAL MOVING MEANS OPERABLE TO PERMIT RELATIVE ROTATABLE MOVEMENT THEREBETWEEN ABOUT THE AXIS OF SAID SHELL, AND DRIVE MEANS OPERABLE TO EFFECT SUCH RELATIVE ROTATION THEREBETWEEN, IMPARTING TO AT LEAST A SUBSTANTIAL PORTION OF SAID GRINDING BODIES ARCUATE TUMBLING MOVEMENT ABOUT THE AXIS OF SAID MILL AND OSCILLATORY AXIAL MOVEMENTS OF SUBSTANTIAL EXTEND IN OPPOSITE DIRECTIONS WITH RESPECT TO THE LONGITUDINAL AXIS OF SAID MILL. 